Controlled source electrical motor speed system



March 14, 1967 J. G. SAFAR 3,309,595

CONTROLLED SOURCE ELECTRICAL MOTOR SPEED SYSTEM Filed March 2, 1964 2 Sheets-Sheet 1 a J 4 L r T-N Z2 3o 24/ 77 ,'L *,::';;i' 5o L f 5r; v x15 12 84 8' --8O @9/78 w 7/ g 75 55 INVENTOR JOHN GSAFAR BY m AT TOR N EY March 14, 1967 Filed March 2, 1964 J. G. SAFAR CONTROLLED SOURCE ELECTRICAL MOTOR SPEED SYSTEM 2 Sheets-Sheet 2 5 k Z M?) /Z/ BY {M 1 ATTORNEY United States Patent Filed Mar. 2, 1964, Ser. No. 348,656 5 Claims. Cl. 318328) The present invention relates to an electrical control system, and more particularly to an automatic, continuous control system wherein electrical signals to a plurality of circuits may be controlled alternatively or simultaneously.

Systems automatically controlling'the time and magnitude of current flowing through various circuits have numerous uses both in the laboratory and industry. Expansion of industrial activities, mechanism of manufacture, and automation of industrial processes have greatly increased the use of electric machines and have placed greater demands on their control systems. Accordingly, as means of illustration, the present invention will be disclosed in reference to its application as a device for continuously and automatically controlling the speed of an electric motor over a very broad speed range" by controlling both the field and armature excitation of the motor. The same system also controls the torque and horsepower of the machine while controlling the speed. However,

those skilled in the art will perceiveother applications for the control system. I

It is well known in the speed control art that low speed control may be accomplished by controlling the armature excitation or the field excitation; but, on the other hand, high speeds may be controlled most effectievly through field excitation. Also, the choice of armature or field control may depend on whether one desires constant torque, in which case the armature excitation is varied and the field excitation held constant; or constant horsepower, in which case the field excitation is varied and the armature excitation held constant. As previously mentioned, high speeds are controlled most effectively by controlled variations in field excitation while maintaining a constant armature excitation; thereby, resulting in constant horsepower and variable torque operation. There are also many applications where it is desirable that at low speed operation the motor horsepower be held constant and the torque controlled by varying the field excitation as is done at high speeds. There are further applications for machines capable of operating at a constant torque through a certain select range of speeds and then cross over and operate at a constant horsepower throughout a second select speed range.

The need for such a versatile, broad-range control is satisfied by the automatically controlled cross-over network of the present invention. This invention provides a new circuit which will allow armature control throughout a portion of the motor speed range, field control throughout another portion of the motor speed range, and an automatic cross over from one type of control to the other at a predetermined voltage which is directly related to speed. The circuit permits variations in the predetermined cross-over speed so that an operator can make adjustments according to the requirements of the specific application. Furthermore, the circuit can be preset so that the motor crosses over from a constant torque operation to a constant horsepower operation, or from constant horsepower to constanttorque depending upon the needs of the specific application.

The cross-over network incorporating the principles of this invention is illustrated in connection with a closedloop motor control system. The system includes a controllable power source which supplies electrical excitation to the armature windings of an electric motor. The

"ice

system also includes a controllable power source which supplies electrical excitation to the field windings of the motor.

ture and field windings of the motor. The speed at which the motor crosses over from constant torque operation to constant horsepower operation or from constant horsepower operation to constant torque operation is controlled by holding the field excitation constant during constant torque operation and holding the armature excitation constant during constant horsepower operation. The cross over network incorporating the principles of this invention provides circuitry whereby the cross-over speed can be preset, and when the motor speed reaches the preset value, cross over occurs automatically. The invention permits the use of static components such as diodes and resistors; there-by, providing a compact, rugged and economi-cal device. The use of static components further increases the utility of the network in undesirable atmospheres, since these components can be easily and economically sealed off from moisture and other foreign particles of the atmosphere.

Accordingly, it is an object of the present invention to provide a circuit which automatically controls the electrical power supplied to a single or plurality of electrical circuits.

It is another object of the present invention to provide a circuit which automatically controls the current through a single or plurality of electrical circuits.

It is another object of the present invention to provide a circuit which simultaneously controls the magnitude and timing of electrical signals applied to a single or plurality of electrical devices.

It is another object of the present invention to provide a cross-over network for electrical machines which automatically, simultaneously and alternatively controls the field and armature excitation of said machine.

It is a further object of the present invention to provide a circuit capable of being utilized as a cross-over network for an electrical machine and which is compact, reliable, efficient and economical.

The foregoing and other objects will appear in the description to follow. In the description, reference is made to the accompanying drawings which form a part hereof in which there is shown by means of illustration specific embodiments in which this invention may be practiced. These embodiments will be described in sufiicient detail to enable those skilledin the art to practice this invention, butit is to be understood that other embodiments of the invention may be used and changes may be made in the embodiments described without departing from the scope of the invention. Consequently, the following detailed description is not to be taken in a limiting sense; instead, the scope ofthe present invention is best defined by the appended claims.

In the drawings:

FIG. 1 is a schematic diagram of an embodiment of the present invention used with a speed control system whereby the excitation of the armature and field windings of a shunt-wound direct current motor are controlled.

FIG. 2 is a schematic diagram of an embodiment of the present invention used 'with a rmotor-generator drive system whereby the field winding excitation of a generator and the armature lwinding excitation of a motor are controlled.

FIG. 1 diagrammatically illustrates a control system incorporating an embodiment of the present invention and designed to automatically and continuously control the speed and the cross over of a direct current motor. The system comprises eight general elements: a power source; a controllable armature excitation source; a

Automatic and continuous speed control is ob tained by controlling the electrical excitation to the armacontrollable field excitation source; a control element for controlling the armature excitation source; a control element for controlling the field excitation; a direct current voltage reference supply; a cross-over network; and a feedback system.

Referring specifically to FIG. 1, the machine to be controlled consists of a direct current motor 1 having a pair of armature terminals 2 and 3, and a field winding 4. The armature terminals 2 and 3 are connected such that the potential at the terminal 3 is positive with respect to the potential at the other terminal 2.

The power source supplying the necessary power to operate the devices of the system includes a pair of power lines 5 and 6.

The controllable armature excitation source includes a controllable power supply 7 diagrammatically represented in block form and providing a direct current voltage out-put. The controllable power supply 7 has a pair of power input terminals 8 and 9 which are connected across the power lines 5 and 6, respectively. The direct current voltage output of the power supply 7 appears across a pair of output terminals 10 and 1-1 with the potential at the terminal 11 being positive with respect to the potential at the terminal 10. The output terminals 10 and 1-1 are connected to the armature terminals 2 and 3, respectively, and a pair of terminals 12 and 13. The controllable power supply 7 also has a pair of input terminals 14 and 15 to receive a control signal which controls the output of the power supply.

The controllable field excitation source includes a controllable power supply 29 diagrammatically represented in block and providing a direct current voltage output. The power supply has a pair of power input terminals 21 and 22 connected across the power lines 5 and 6, respectively. The output of the power supply Zti appears across a pair of output terminals 23 and 24. The output terminal 23 is connected directly to the field winding 4 and the output terminal 24 is connected to a conventional feedback circuit 25 diagrammatically represented in block form. The feedback circuit 25 is connected in series with the terminal 24 and the field winding 4 at an input terminal '26 and an output terminal 27. The output of the feedback circuit 25 appears across a pair of output terminals 28 and 29. The controllable power supply 20 also has a pair of input terminals 30 and 31 to receive a control signal which controls the ouput of the power supply.

The control element for controlling the armature excitation source includes a conventional control element 35 diagrammatically represented in block form. The control element '35 has a pair of power input terminals 36 and 37 connected across the power lines 5 and 6, respectively. The output of the control element 35 appears across a pair of output terminals 38 and 39 which are respectively connected across the control input terminals 14- and 15 of the controllable power supply 7. The control element 35 also has a pair of input terminals 40 and 41 to receive armature control signals.

The control element for controlling the field excitation source includes a conventional control circuit 45 diagrammatically represented in block form. The control element 45 has a pair of power input terminals 46 and '47 connected across the power lines 5 and 6, respectively. The output of the control element 45 appears across a pair of output terminals 4 8 and 49 which are respective ly connected across the control input terminals 30 and 31 of the controllable power supply 20. The control element 45 also has a pair of input terminal blocks having the general reference characters 50 and 51 to receive control signals. The input terminal block 50 diagrammatically represented by a broken-line block includes a set of terminals 52, 53 and S4. The input terminal block 51 diagrammatically represented by a broken-line block includes a set of terminals 55, 56 and 57.

The direct current voltage reference supply element of the system consists of a conventional rectifier 60 diagrammatioaliy represented in block form. The rectifier 6!) has a pair of power input terminals 61 and 62 connected across the power lines 5 and 6, respectively. The rectifier 60 has a pair of output terminals 63 and d4 of which the potential at the terminal 63- is positive with respect to the potential at the terminal 64. The output terminals 63 and 64- are also connected across a signal magnitude sensitive device in the form of a breakdown diode 65 the cathode of which is connected to the terminal 63 and the anode to the terminal 64.

The cross-over network element of the system consists of a reference signal source in the form of a potentiometer 70 having a pair of fixed terminals 71 and 72 respectively connected across the output terminals 63 and 64 of the rectifier 6%. The fixed terminal 71 is also connected to the terminal 55 of the input terminal block 51 of the control element 45. A movable contact 73 of the potentiometer 70 is connected to the terminal 52 of the input terminal block 50 of the control element 45. A second reference signal source in the form of a speed control potentiometer 74 having a pair of fixed terminals 75 and 76 is connected across the output terminals 63 and 64, respectively. A movable contact 77 of the speed control potentiometer 74- is connected to a signal magnitude sensitive device in the form of a breakdown diode 78 with the cathode of the breakdown diode connected to the movable contact. The anode of the breakdown diode 73 is connected to a clamipng network in the form of variable resistance 79 having a fixed terminal $0 and a movable contact 81 and a blocking diode 82.

The fixed terminal fit) is connected to the anode of the breakdown diode 78. The movable contact "81 of the variable resistance 79 is connected to the anode of the blocking diode 52. The cathode of the blocking diode $2 is connected to the terminal 53 of the input terminal block 50 of the control element 45. The movable contact 77 of the potentiometer 74 is also connected to a signal magnitude sensitive device in the form of a breakdown diode 83. The cathode of the breakdown diode 83 is connected to the movable contact 77 and the anode is connected to the negative otuput terminal 64 of the rectifier 60. The feedback circuit 25 is also connected through a correcting signal source which corrects for nonlinearities in field decreasing control and having a polarity opposite to that of the feedback signal of the feedback circuit 25. In PEG. 1, this correcting signal source is represented in the form of a potentiometer 35 having a pair of fixed terminals 84 and 86 with the terminal 84 connected to the output terminal 64 of the rectifier 60 and the terminal 86 connected to the terminal 54 of the input terminal block 50. A movable contact 87 of the potentiometer is connected to the output terminal 29 of the feedback source 25, thus completing the circuit of the cross-over network.

The feedback element of the system consists of the feedback circuit 25 previously described in connection with the controllable field excitation source and also, a potentiometer 90 having a pair of fixed terminals 91 and 92 and a movable contact 93. The potentiometer 90 is connected in series with the armature terminals 2 and 3 of the motor ll such that the feedback signal across the potentiometer 90 varies with speed variations. The terminal 92 is connected to the negative output terminal 64 of the rectifier 60. The movable contact 93 is connected to the control signal input terminal 41 of the control element 35, such that the net signal across the breakdown diode 83 is equal to the algebraic sum of the feedback signal and the reference signal across the fixed terminal 76 and the movable contact 74 of the speed control potentiometer 74. Therefore, a the motor 1 approaches the desired speed set according to the setting of the potentiometer 74, the net reference signal source applied across the breakdown diode 83 progressively increases until the motor reaches the predetermined speed. Furthermore, when the net reference signal source exceeds the breakdown of the breakdown diode 83, the potential across the diode remains constant. Also, depending on the setting of the clamping network incorporating diode 82 and variable resistance 81 and the breakdown characteristics of breakdown diode 78, the value of the net reference signal determines when current flows through the terminals 53 and 56 of the terminal blocks 50 and 51. p

The theoretical operation of the above-described system is believed to be as hereinafter set forth. The power necessary to operate the various devices of the system appears across the lines 5 and 6.

The controllable armature excitation source, which along with the controllable field excitation source represents a device to be controlled by the control circuit provides power for the armature winding terminals 2 and 3. The magnitude of the excitation is controlled by the control signal appearing across the input terminals 14 and 15. i

The controllable power supply 7 may be any one of numerous available devices and therefore is diagrammatically represented in block form. Those skilled in the art will recognize that there are numerous static and electronic circuits which maybe utilized in combination with a power source to supply excitation to the armature terminals, and which may also be controlled such that the magnitude of the excitation is proportional to a control signal. The controllable power supply 7 receives its input power at the terminals 8 and 9 and provides direct current voltage across the output terminals 10 and 11 with the potential at the terminal 11 positive with respect to the potential at the terminal 18. The control signal received at the control terminals 14 and 15 control the amount of power delivered to the output terminals 10 and 11 and to the armature terminals 2 and 3.

The rotational speed of the motor 1 is directly proportional to the armature excitation. Therefore, controlled increases or decreases in the armature excitation results in corresponding controlled increases or decreases in the speed of the direct current motor 1. Furthermore, by cont-rolling the field excitation such that it retains a constant value while the armature excitation is varied, the torque of the motor remains constant while the horsepower varies.

The speed of the direct current motor 1 is also controlled by controlled variations of the excitation applied to the field winding 4. Accordingly, the controllable field excitation source represents a second device of FIG. 1 to be controlled. Controlled speed variations is accomplished by decreases in the field excitation which results in controlled increases in speed, and by controlled increases in the field excitation which results in controlled decreases in speed. The excitation to the field winding 4 is controlled in a manner similar to that in which the armature excitation is controlled. The controllable power supply acts in a manner similar to that of the controllable power supply 7, and may include similar characteristcs. Furthermore, by controlling the armature excitation such that it retains constant value while the field excitation is varied, the horsepower of the motor remains constant while the torque varies.

It is commonly known that decreases in field excitation of a direct current motor has a substantially greater effect on the speed range than that where the field excitation is held constant and the armature excitation increased. There are several direct current motors available wherein the speed range during constant field excitation and varying armature excitation i one-fourth or one-third that where the armature excitation is held constant and the field excitation decreased. Accordingly, since during constant field excitation the motor acts at a constant torque and during constant armature excitation at a constant horsepower, by controlling both the armature excitation and the field excitation the motor can be utilized as a constant torque machine over a specific speed range and then 6 switch over and act as a constant horsepower machine over another specific speed range.

The control circuit or cross-over network as so previously refer-red to in FIG. 1, provides a means whereby an operator can preset the speed control potentiometer 74 to a voltage corresponding to a desired speed and the motor will operate at the desired speed automatically. Furthermore, the maximum desired operating speed can be controlled by presetting the clamping network to a voltage corresponding to the desired maximum speed. Also, the speed of the motor at which the operator desires a cross-over from constant torque operation to constant horsepower operation can be controlled by selection of the breakdwn diodes 78 and 83 and setting the potentiometer 74 and the variable resistance 79 to correspond to the desired cross-over speed.

During constant torque operation, a portion of the constant direct current reference signal appearing across the potentiometer 70 is applied to the control element 45 at the terminals 52 and 55, while the breakdown diode 78 blocks current flow, thereby retaining the field excitation at a constant value. At the same time the control signal to the control element for the controllable armature excitation source varies according to the magnitude of the signal appearing across the breakdown diode 83. At the point that the magnitude of the varying signal attains or exceeds the breakdown value of the breakdown diode 83, the control signal to the controllable armature excitation source remains constant and thereafter the machine operates with constant horsepower.

A portion of the signal appearing across the diode 83, depending on the setting of the variable resistance 79, is also applied across the breakdown diode 78. The'point at which the value of the signal across the breakdown diode 78 reaches the breakdown value of the diode 78, the control element 45 controlling the controllable field excitation source receives a second direct current signal at the terminals 53 and 56. This direct current signal opposes the first signal applied to the terminals 52 and 55, thus decreasing the field excitation. This second signal to the control element 45 varies proportionally to variation in the voltage appearing across the breakdown diode 83.

The control elements 35 and 45 receive the control signals and provide proportional output signals across the output terminals 38, 39 and 48, 49, which in turn control the armature and field excitations. The circuitry of the control elements 35 and 45 is dependent upon the means in which the outputs of the controllable powersupplies 7 and 20 are controlled. For example, if the power supplies utilize siliconcontrolled rectifiers, the signal appearing across the input terminals 14, 15 and 3t), 31 need be pulses. However, since the signals at the input terminals 40, 41, and 5t), 51 of the control elements 35 and 45 are direct current signals, these signals need be converted to pulses by the control elements 35 and 45.

Those skilled in the art will readily recognize that there are numerous available means of controlling the output of the controllable power supplies 7 and 20 and that there are also numerous ways in which to convert the direct current signals supplied by the control element to accommodate the specific requirements.

The breakdown voltage of the breakdown diode 65 determines the range over which the breakdown diode 78 and the variable resistance 79 have control. For example, ifthe breakdown diode 65 has a breakdown voltage of one hundred volts and the breakdown diodes 78 and 83 have a breakdown voltage of fifty volts, and if the potentiometers 74 and 85 are preset such that the entire voltage across the breakdown diode 65 appears across the diodes 78 and 83 as a reference signal source, the armature excitation will vary according to variations in the reference source until it reaches fifty volts. Also, during this period the breakdown diode 78 blocks current flow and the signal across the terminals 52 andf55 holds the field excitation at a constant level. After the reference signal exceeds fifty volts, the signal across the breakdown diode 83 remains at fifty volts and the breakdown diode 78 conducts. The potential across the terminals 53 and 56 increases with increases in the reference signal. However, when the reference signal reaches one hundred volts, the breakdown diode 65 breaks down thereby preventing further increases in the signal across the terminals 53 and 56.

The speed range of the motor can be increased by incorporating a breakdown diode 65 possessing a higher breakdown rating. For example, if in the previous illustration the breakdown diode 65 had a breakdown rating of one hundred and fifty volts the potential across the terminals 53 and 56 would be variable until the reference signal reached one hundred fifty volts.

The third signal at the input terminal blocks 50 and 51 has a value equal to the difference between the signal appearing across the output terminals 28 and 29 of the feedback circuit 25 and the predetermined fixed direct current correcting signal source appearing across the movable contact 87 and the fixed contact 86 of the potentiometer 85. This third signal corrects for non-linearities in the decreasing field which may result from increases in the reference potential after the machine crosses over from constant horsepower to constant torque operation. Also, the feedback provides a means for maintaining the field excitation at a constant level during the period in which the armature excitation is in control.

As previously mentioned, those skilled in the art will readily recognize that there are numerous devices which may be utilized to satisfy the needs of the control elements 35 and 45. Obviously, the circuitry of the control element depends upon the circuitry of the power supply to be controlled. As means of illustration, of the numerous devices available for use in connection with power supplies incorporating gas tubes or silicon controlled rectifiers: magnetic amplifiers; reed switches or other mechanical devices; resistance-inductance or resistance-capacitor circuits with a phase-shift reactor; and transistor circuits comprising a unijunction relaxation oscillator or a unijunction resistance-capacitor can be utilized. The control element 45 shows a pair of terminal blocks 50 and 51 for separate terminals therein. Instances in which a magnetic amplifier is utilized, the terminals 52 and 55 may represent opposite terminals of a bias winding, the terminals 53 and 56 may represent opposite terminals of a second winding opposing the bias winding, and the terminals 54 and 57 may represent opposite terminals of a third winding for a feedback signal.

The versatility and utility of the principles of this invention are further illustrated in FIG. 2 wherein they are incorporated in a motor-generator control system. The system incorporates a prime mover which causes a direct current generator to rotate and generate a voltage which in turn is applied to the armature winding of the motor. In this illustration the excitation applied to the armature winding is controlled by controlled variations in the field excitation of the direct current generator. Several elements of the system are common to those illustrated in FIG. 1. Accordingly, as a matter of convenience those elements which are common will carry the same reference numerals as in FIG. 1. The direct current motor 1, having the armature terminals 2 and 3 and the field winding 4 is the same as that previously described. Also, the control elements 35 and 45 for controlling the field and armature excitation sources, the direct current voltage reference supply, the cross-over network or control circuit, and the feedback source are all common.

The power source of FIG. 2 includes the power lines and 6 as shown in FIG. 1 and a set of three-phase power lines 110, 111 and 112. The power source further includes a prime mover represented by a synchronous alternating current motor 113. The motor 113 is con- 8 nected across the power lines 110, 111 and 112 through a starter motor comprising a set of main contacts 114, 115 and 116; a corresponding set of overload relays 117, 118 and 119; an overload relay contact 1211; a coil 121; a pushbutton station consisting of a pair of pushbutton switches 122 and 123. The relay contact 120, the coil 121 and the pushbutton switches 122 and 123 are connected across the single phase power lines 5 and 6.

The controllable armature excitation source consists of a direct current generator having a rotor 131 connected to the synchronous alternating current motor 113 by a mechanical coupling 132. The generator 139 has a pair of armature winding terminals 133 and 134 which are connected across the armature terminals 2 and 3, respectively, of the direct current motor 1. A field winding 135 of the direct current generator 130 is connected in parallel with a diode 136, the anode of the diode 136 is connected to an output terminal 137 of a conventional full-wave rectifier 138 diagrammatically represented in block form. A pair of power input terminals 139 and 140 of the rectifier 138 are connected to the power lines 5 and 6, respectively. A second output terminal 141 of the full-wave rectifier 138 is connected to a silicon controlled rectifier 142. The cathode of the silicon controlled rectifier 142 is connected to the cathode of the diode 136 and to the field winding 135. A gate lead 143 of the rectifier 142 is tied to the output terminal 38 of the control element 35. The cathode of the silicon controlled rectifier 142 is connected to the output terminal 39 of the control element 35.

The controllable field excitation source consists of a diode connected across the field winding 4 of the direct current motor 1. The anode of the diode 150 is also connected to an output terminal 151 of a conventional full-wave rectifier 152 diagrammatically represented in block form. The cathode of the diode 150 is connected to the output terminal 27 of the feedback circuit 25. The full-wave rectifier 152 has a pair of power input terminals 153 and 154 connected across the power lines 5 and 6, respectively. A second output terminal 155 of the full-wave receifier 152 is connected to the anode of a silicon-controlled rectifier 156. The gate lead 157 of the silicon controlled rectifier 156 is connected to the output terminal 48 of the control element 45. The cathode of the silicon controlled rectifier 156 is connected to the input terminal 26 of the feedback circuit 25. The remainder of the diagram of the system illustrated in FIG. 2 is the same as that of FIG. 1 and therefore will not be further described.

The theoretical operation of the system illustrated in FIG. 2 is believed to be as hereinafter set forth. At the time the system is to be operated the pushbutton switches 122 and 123 are closed as to apply power to the synchronous motor 113 through the motor starter comprising the main contacts 114, 115 and 116. The synchronous motor 113 in combination with the mechanical coupling 132 causes the direct current generator 130 to rotate at a constant speed. Therefore, since the magnitude of the output voltage of a direct current generator is dependent upon the rotational speed and the field excitation, control of the output potental appearing at the terminals 133 and 134 is controlled by controlling the excitaiton applied to the field winding 135.

Control of the excitation applied to the field winding 135 is accomplished by the control signal received between the gate lead 143 and the cathode of the silicon controlled rectifier 142 from the control element 35. In the absence of a control signal, the full-wave output potential of the rectifier 13S appears across the silicon controlled rectifier 142 and current flow through the field winding 135 is blocked. Upon receiving a positive pulse the silicon controlled rectifier 138 conducts thereby causing current to flow through the field winding 135. The silicon controlled rectifier 138 continues to conduct for the remainder of the half cycle and when the output potential reaches zero, conduction ceases. Conduction commences when another positive pulse is received at the gate. Therefore, by controlling the time during the half cycle of the rectified voltage at which the gate lead 143 receives a positive pulse the current passing through the field winding 135 is controlled.

Likewise, the excitation of the armature winding 4 is controlled by controlling the conduction time of the silicon controlled rectifier 156 which is connected between the output terminals of the full-wave rectifier 152 and the armature winding 4. The conduction time is controlled by the pulse signals received between the gate lead 157 and the cathode of the silicon conrolled rectifier 156.

The diodes 136 and 150 act as back diode and conduct inductive currents created by field windings 4 and 136 of the motor 1 and generator 130, respectively, during the period when the silicon controlled rectifiers 142 and 156 are called upon the block current flow. In the absence of the diodes, inductive currents would continue to flow through the silicon conrolled rectifiers at the time that the applied voltage reached zero, and -in turn preventing the silicon controlled rectifiers from regaining control.

Those skilled in the art will readily recognize that there are numerous full-wave rectifiers available which may be utilized for the purposes of this system. Furthermore, as previously mentioned, the control elements 35 and 45 may be any one of numerous available circuits.

The foreging illustrative embodiments are indicative only of the many applications of the control circuit described herein. In machine controls, the qualities to be controlled may include position, acceleration, voltage, frequency, etc. Furthermore, there are numerous applications in electronics circuitry for such a control circuit. Accordingly, the scope of the invention should be determined from the following claims rather than from the embodiments selected for illustrative purposes.

I claim:

1. A speed control network for simultaneously controlling the electrical excitation of the armature and field windings of an electrical motor comprising, in combination:

a first controllable electric power source adapted to provide electrical excitation to an armature winding of an electrical motor;

a second controllable electric power source adapted to provide electrical excitation to a field winding of an electrical motor;

a first control element, the first control element being responsive to a net armature control signal and controlling the first power source in accordance with said armature control signal;

a second control element, the second control element being responsive to a net field control signal and controlling the second power source in accordance with said second control signal;

an armature feedback sensing means adapted to provide an electrical armature feedback signal in accordance with the actual armature excitation of said electrical motor;

a direct current voltage reference supply source;

a cross-over network providing control signals for said first and second control elements, the cross-over network including a first present field reference signal source responsive to said reference supply source and providing a substantially constant first field control signal segment to said second control element, a second variable field reference signal source responsive to said reference supply source and preset according to the desired motor speed and connected to said second control element in series with a first unidirectional signal magnitude sensitive device, said first signal magnitude sensitive device having breakdown voltage characteristics coinciding with the desired cross-over speed, said first signal magnitude sensitive device substantially blocking current flow for potentials less than the breakdown value, a second unidirectional signal magnitude sensitive device extending across said reference supply source and extending in series with said armature feedback sensing means and the first control element, said second signal magnitude sensitive device having voltage breakdown characteristics coinciding with the desired crossover speed, whereby for motor speeds below the cross-over value the net field control signal remains substantially constant comprising substantially the preset value of the first field control signal segment and the armature control signal value varies in accordance with the signal across said second magnitude sensitive device and said armature feedback signal and for motor speeds exceeding the cross-over value the net field control signal comprises substantially the summation of the first and second field control signal segments and the armature control signal value remains substantially constant in accordance with the breakover voltage value of said second magnitude sensitive device and said armature feedback signal.

2. A speed control network in accordance with claim 1 further including a field feedback sensing means adapted to provide an electrical field feedback signal segment to the second control element in accordance with the actual field excitation of said electrical motor.

3. A speed control network in accordance with claim 1 further including a clamping network comprising a variable resistor connected in series with said first signal magnitude sensitive device and said second control element, said clamping network being preset in accordance with desired motor speed.

4. A speed control network in accordance with claim 1 further including a third unidirectional magnitude sensitive device extending across the direct current voltage reference supply source, and having breakdown characteristics coinciding with the desired maximum desired reference supply.

5. A speed control network for simultaneously controlling the electrical excitation of the armature and field windings of an electrical motor comprising, in combination:

a first controllable electric power source adapted to provide electrical excitation to an armature winding of an electrical motor;

a second controllable electric power source adapted to provide electrical excitation to a field winding of an electrical motor;

a first control element, the first control element being responsive to a net armature control signal and controlling the first power source in accordance with said armature control signal;

a second control element, the second control element being responsive to a net field control signal and controlling the second power source in accordance with said second control signal;

an armature feedback sensing means adapted to provide an electrical armature feedback signal segment in accordance with the actual armature excitation of said electrical motor;

a direct current voltage reference supply source;

a cross-over network providing control signals to the first and second control elements for maintaining the field excitation substantially constant over a first predetermined motor speed range and the armature excitation substantially constant over a second motor speed range, the cross-over network including a first potentiometer having a pair of fixed terminals extending across the voltage reference supply source and an adjustable contact extending to the second control element and providing a preset first substantially constant field, control signal segment, a second 11 potentiometer having a pair of fixed terminals extending across the voltage reference source and an adjustable contact extending in series with a first unidirectional breakdown diode to the second control 12 across said second diode and said armature feedback signal and for motor speeds exceeding the cross-over value, the net field control signal comprises substantially the summation of the first and second field conelement providing a second field control signal seg- 5 trol signal segments and the armature control signal ment, said first diode having breakdown voltage charvalue remains substantially constant in accordance acteristics coinciding with the desired cross-over with the breakover value of said second diode and speed, a second unidirectional breakdown diode eX- said armature feedback signal.

tending across the input to said first control element in series with the armature :feedback sensing means 10 References Cited y the Examine! and across said adjustable contact of said second potentiometer and the voltage reference source, said UNITED STATES PATENTS second diode having breakdown voltage characteris- 3022453 2/1962 miles 318 146 X 3,108,214 10/1963 Wilkerson 318144 tlcs COll'lCldlng with the desired cross-over speed,

whereby for motor speeds below the cross-over value 15 3219300 11/1965 Wflkerson 318*146 X the net field signal remains substantially constant I comprising substantially the preset value of the first ORIS RADER E xammer' field control signal segment and the armature con- J. C. BERENZWEIG, Assistant Examiner. trol signal value varies in accordance with the signal 

1. A SPEED CONTROL NETWORK FOR SIMULTANEOUSLY CONTROLLING THE ELECTRICAL EXCITATION OF THE ARMATURE AND FIELD WINDINGS OF AN ELECTRICAL MOTOR COMPRISING, IN COMBINATION: A FIRST CONTROLLABLE ELECTRIC POWER SOURCE ADAPTED TO PROVIDE ELECTRICAL EXCITATION TO AN ARMATURE WINDING OF AN ELECTRICAL MOTOR; A SECOND CONTROLLABLE ELECTRIC POWER SOURCE ADAPTED TO PROVIDE ELECTRICAL EXCITATION TO A FIELD WINDING OF AN ELECTRICAL MOTOR; A FIRST CONTROL ELEMENT, THE FIRST CONTROL ELEMENT BEING RESPONSIVE TO A NET ARMATURE CONTROL SIGNAL AND CONTROLLING THE FIRST POWER SOURCE IN ACCORDANCE WITH SAID ARMATURE CONTROL SIGNAL; A SECOND CONTROL ELEMENT, THE SECOND CONTROL ELEMENT BEING RESPONSIVE TO A NET FIELD CONTROL SIGNAL AND CONTROLLING THE SECOND POWER SOURCE IN ACCORDANCE WITH SAID SECOND CONTROL SIGNAL; AN ARMATURE FEEDBACK SENSING MEANS ADAPTED TO PROVIDE AN ELECTRICAL ARMATURE FEEDBACK SIGNAL IN ACCORDANCE WITH THE ACTUAL ARMATURE EXCITATION OF SAID ELECTRICAL MOTOR; A DIRECT CURRENT VOLTAGE REFERENCE SUPPLY SOURCE; A CROSS-OVER NETWORK PROVIDING CONTROL SIGNALS FOR SAID FIRST AND SECOND CONTROL ELEMENTS, THE CROSS-OVER NETWORK INCLUDING A FIRST PRESENT FIELD REFERENCE SIGNAL SOURCE RESPONSIVE TO SAID REFERENCE SUPPLY SOURCE AND PROVIDING A SUBSTANTIALLY CONSTANT FIRST FIELD CONTROL SIGNAL SEGMENT TO SAID SECOND CONTROL ELEMENT, A SECOND VARIABLE FIELD REFERENCE SIGNAL SOURCE RESPONSIVE TO SAID REFERENCE SUPPLY SOURCE AND PRESET ACCORDING TO THE DESIRED MOTOR SPEED AND CONNECTED TO SAID SECOND CONTROL ELEMENT IN SERIES WITH A FIRST UNIDIRECTIONAL SIGNAL MAGNITUDE SENSITIVE DEVICE, SAID FIRST SIGNAL MAGNITUDE SENSITIVE DEVICE HAVING BREAKDOWN VOLTAGE CHARACTERISTICS COINCIDING WITH THE DESIRED CROSS-OVER SPEED, SAID FIRST SIGNAL MAGNITUDE SENSITIVE DEVICE SUBSTANTIALLY BLOCKING CURRENT FLOW FOR POTENTIALS LESS THAN THE BREAKDOWN VALUE, A SECOND UNIDIRECTIONAL SIGNAL MAGNITUDE SENSITIVE DEVICE EXTENDING ACROSS SAID REFERENCE SUPPLY SOURCE AND EXTENDING IN SERIES WITH SAID ARMATURE FEEDBACK SENSING MEANS AND THE FIRST CONTROL ELEMENT, SAID SECOND SIGNAL MAGNITUDE SENSITIVE DEVICE HAVING VOLTAGE BREAKDOWN CHARACTERISTICS COINCIDING WITH THE DESIRED CROSSOVER SPEED, WHEREBY FOR MOTOR SPEEDS BELOW THE CROSS-OVER VALUE THE NET FIELD CONTROL SIGNAL REMAINS SUBSTANTIALLY CONSTANT COMPRISING SUBSTANTIALLY THE PRESET VALUE OF THE FIRST FIELD CONTROL SIGNAL SEGMENT AND THE ARMATURE CONTROL SIGNAL VALUE VARIES IN ACCORDANCE WITH THE SIGNAL ACROSS SAID SECOND MAGNITUDE SENSITIVE DEVICE AND SAID ARMATURE FEEDBACK SIGNAL AND FOR MOTOR SPEEDS EXCEEDING THE CROSS-OVER VALUE THE NET FIELD CONTROL SIGNAL COMPRISES SUBSTANTIALLY THE SUMMATION OF THE FIRST AND SECOND FIELD CONTROL SIGNAL SEGMENTS AND THE ARMATURE CONTROL SIGNAL VALUE REMAINS SUBSTANTIALLY CONSTANT IN ACCORDANCE WITH THE BREAKOVER VOLTAGE VALUE OF SAID SECOND MAGNITUDE SENSITIVE DEVICE AND SAID ARMATURE FEEDBACK SIGNAL. 